1. Field of the Invention
The present invention relates to an image heating apparatus suitable for use as an image heating/fixing apparatus (fixing device) mounted to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer.
2. Description of the Related Art
An image forming apparatus such as an electrophotographic copying machine or printer is required to have higher image quality, and therefore, a density of a recording resolution becomes higher and higher to be 1200 dpi, 2400 dpi, 3600 dpi and the like.
In the above-mentioned image forming apparatus, light is radiated by a laser beam onto an outer peripheral surface (surface) of a drum-shaped electrophotographic photosensitive member (hereinafter, referred to as photosensitive drum). An image (electrostatic latent image) is recorded onto a surface of the photosensitive drum by the amount of radiated light at that time. On the surface of the photosensitive drum, all types of images ranging from a binary image such as a character to an image containing a halftone such as a picture can be formed. For reproducing a neutral density at this time, an image processing technique such as a pulse-width modulation system (PWM system), a dither method or a density pattern method is used to enable the formation of various patterns on the surface of the photosensitive drum.
Moreover, for the above-mentioned image forming apparatus, the reproducibility of a fine line pattern such as a small point size character becomes an issue with a recent increase in recording density and a recent demand for higher image quality. On the other hand, when the image containing the halftone such as the picture is output on a high-gloss recording material such as coated paper, an output of a high-gloss image at a gloss level close to that of the recording material with little unevenness in gloss is an issue. In order to resolve the issues, various technologies have been proposed.
Japanese Patent Application Laid-Open No. 2004-139039 describes a fixing device including heating and temporarily fixing means and image gloss control means. The heating and temporarily fixing means provides at least heat for a recording material, on which an unfixed toner image is formed, to soften or melt a toner of the unfixed toner image. Then, while the toner image is in a deformable state by an external force, the image gloss control means pressurizes the toner image without heating to gloss the toner image. Moreover, for keeping a temperature of the image gloss control means constant when images are continuously output, the temperature of the image gloss control means is controlled to be kept to a given temperature or lower by cooling means such as a cooling fan.